1. Field of the Invention
The present invention relates to a method for manufacturing a laser beam transmitting member, a resin molding apparatus and a method for manufacturing a composite resin product.
2. Description of Related Art
Conventionally, a method for manufacturing a composite resin product by molding resins into a laser beam transmitting member and a laser beam absorbing member and welding the two members with a laser beam has been proposed (JP 2001-71384, for example).
When a laser beam transmitting member is a cap that covers a hole in a laser beam absorbing member or the like, a method, for example, shown in FIG. 19A or FIG. 20A is adopted. According to such a method, a welding target part 1a along an annular virtual curve L of a laser beam transmitting member 1 is irradiated with laser beams and the laser beams that have been transmitted through the welding target part 1a are absorbed by a laser beam absorbing member 2. The part of the laser beam absorbing member 2 that has absorbed the laser beams melts and the heat of the molten resin melts the part 1a of the laser beam transmitting member 1, and thus the two members 1 and 2 are welded to each other.
A metal mold 4 for molding a resin into the laser beam transmitting member 1, to be welded with a laser beam as shown in FIG. 19A, is shown in FIG. 19B. In a cavity 6 of the metal mold 4, a route distance X1 between a part (a welding target molding part) 6a for molding the welding target part 1a and a filling terminal wall 6b is constant. In the metal mold 4, on the other hand, a route distance X2 between each part of the welding target molding part 6a and a gate 5 nearest to the part is not constant. Therefore, the time intervals taken for completely filling a resin into the respective peripheral ends of the welding target molding part 6a differs from part to part. When a crystalline laser beam transmitting member 1 is molded, the shorter the distance X2, that is, the nearer the welding target molding part 6a is to the gate 5, the higher the inclusion rate of crystal (which is the proportion of the volume of the crystal included in a product with respect to the total volume of the product) at the welding target part 1a to be molded, and the transmittance of laser beam becomes lower, accordingly. As a result, when the crystalline laser beam transmitting member 1 molded using the metal mold 4 is welded to the laser beam absorbing member 2, the following problem arises. If, for example, the irradiation energy of a laser beam is determined in accordance with the welding target part 1a molded at a part 6a near to the gate 5, the transmitted laser beam at the welding target part 1a molded at another part 6a far from the gate 5 applies excessively large energy to the laser beam absorbing member 2. When the given energy is excessively large, the molded resin of the laser beam absorbing member 2 is gasified and voids are created at the welding boundary surface, resulting in reduction in the welding strength. Moreover, when the given energy is excessively large, the laser beam absorbing member 2 melts excessively and burrs are produced, resulting in deterioration in the appearance of a compound resin product. On the other hand, if the irradiation energy is determined in accordance with the welding target part 1a molded at a part 6a far from the gate 5, the transmitted laser beam at the welding target part 1a molded at the part 6a near the gate 5 cannot apply sufficient energy to the laser beam absorbing member 2. When the given energy is insufficient, the amount of molten laser beam absorbing member 2 is insufficient, resulting in a reduction in the welding strength.
Next, a metal mold 7 for molding a resin into the laser beam transmitting member 1 to be welded with a laser beam as shown in FIG. 20A is shown in FIG. 20B. In a cavity 9 of the metal mold 7, a route distance Y1 between each part of a part (a welding target molding part) 9a for molding the welding target part 1a and a gate 8 nearest to the part is almost constant. In the cavity 9 of the metal mold 7, however, a route distance Y2 between the welding target molding part 9a and a filling terminal wall 9b is not constant. Therefore, the time intervals taken for completely filling a resin into the respective peripheral ends of the welding target molding part 9a differs from part to part. When the crystalline laser beam transmitting member 1 is molded, the greater the distance Y2, that is, the farther the filling terminal wall 9b is from the welding target molding part 9a, the higher the inclusion rate of crystal at the welding target part 1a to be molded, and the transmittance of the laser beam becomes lower accordingly. As a result, also when the crystalline laser beam transmitting member 1 molded using the metal mold 7 is welded to the laser beam absorbing member 2, poor welding is likely to occur as in the case of the crystalline laser beam transmitting member 1 molded using the metal mold 4.